Lossless Predictive Audio Compression
| Lossless Predictive Audio Coder | |
|---|---|
| Basic data
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| developer | Tilman sweetheart |
| Current version | 3.08 (February 7, 2002) |
| operating system | Linux , Windows , Solaris |
| category | Encoder |
| License | Closed source , freeware |
| German speaking | Yes |
| Institute for Telecommunication Systems : LPAC - Lossless Audio Codec for Windows and Linux (English) | |
Lossless Predictive Audio Compression ( LPAC ; German lossless predictive audio data compression ) is a lossless method for audio compression. It is used in a lossless audio format with the filename extension .pac . It was developed by Tilman Liebchen from the Communications Department at the Technical University of Berlin .
It is now a historical format because it is no longer being developed and has its official successor in MPEG-4 Audio Lossless Coding .
Existing features
In comparisons, the method delivers mediocre packing rates and decodes very quickly. Mono and stereo PCM data are supported with samples resolved in 8, 12, 16, 20 and 24 bit . The compression distinguishes between six compression modes, which differ in compression strength and speed. There was also discussion in LPAC Cyclic Redundancy Check (Engl. Cyclic redundancy check ) implemented.
Missing features
Some contemporary features are missing:
- Tagging (embedding of additional information on the title, author, etc.)
- Streaming
- Multi-channel audio
- Replay gain standards
- Error correction mechanisms ( CRC checksums make defects at least recognizable)
Additional characteristics
- Fast jumping to any position in a file, which must first be activated by an additional option, which then leads to larger files
- Proprietary format
Practical additional options such as the optional separate storage of the forecast signal and an error correction file or self-extracting files (see WavPack ) are also not available.
License, source code
Graphically operable as well as command line programs for Windows , Linux and Solaris as well as a program library (DLL) are available free of charge. However, the source code is not freely available. The MPEG-4 Audio Lossless Coding that emerged from LPAC is - as an open standard - disclosed and described.
history
LPAC is the successor to Lossless Transform Audio Compression (LTAC). Development at LPAC was discontinued at the end of 2004 / beginning of 2005, as a revised version became the MPEG-4 Audio Lossless Coding (ALS) standard in December 2005 . Important features that were previously missing were added and the format was disclosed.
technology
The audio signal is predicted with adaptive linear prediction . The residual signal that includes the deviations from the forecast, then passes through a Rice - entropy coding , which exploits the different probabilities of occurrence of samples of the residual signal.
See also
- MPEG-4 Audio Lossless Coding (successor)
- Lossless Transform Audio Compression (predecessor)